Rotary pump with interacting tri-lobed impellers



' G. R. FUNK May 27, 1958 ROTARY PUMP WITH INTERACTING TRI-LOBED IMPELLERS Filed March 18, 1955 VENTOI Q. TA/K IN 4:4 P

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ATTO/PA/[YS Unite States Patent ROTARY PUMP with mrnRAcrmr; TRI-LOBED rnrnrrnns Gilbert R. Funk, Waaziresha, Wis, assignor to Waukesha Foundry Company, Waukesha, Wis, a corporation of Wisconsin Application March 18, 1955, Serial No. 495,239

3 Claims. (Cl. 103-126) This invention relates to a rotary pump with interacting iii-lobed impellers.

The pump here disclosed is of the general type in which interacting impellers rotate around fixed sleeves as shown in Patent 2,279,136. It is found to be peculiarly suitable for use as a sanitary pump and one of its characteristics is its ability to handle products such as milk without inducing an extensive amount of foaming. However, the speed of operation and the rate of liquid pumped by devices of this type as heretofore known has been distinctly limited. It has been considered impossible to produce a pump of this type in which the impellers have more than two lobes.

The present pump not only has three lobes on each impeller but can be operated at relatively high impeller speeds to have an output which greatly exceeds the output of any pump of this type heretofore known. The results achieved appear to be made possible by the particular mathematical relationship of the parts, including the diameter of the fixed sleeves and the arcuate extent of impeller bearing notches therein, the center distance or spacing between the axes of the impellers and the internal and external diameters of the impellers. These factors, in turn, result in a particular choice of the arcuate extent of the lobes and the provision of a shaft which will have adequate strength in the diameter in which it is necessary to make this shaft consistent with the impeller dimensions required for successful operation.

In the drawings:

Fig. 1 is a view partially in elevation of a pump embodying the invention.

Fig. 2 is a view taken in section on the line 22 of Fig. 1.

Fig. 3 is a view taken in section on the line 33 of Fig. 1.

In the preferred embodiment illustrated, the device comprises a gear housing 4 having a closure cap 5 from which the drive shaft 6 projects. Removably fixed to the opposite end of the gear housing is the pump housing 7 having a closure cap 8. Dowels 9 are used together with bolts 10 to secure and position the pump housing 7 and closure cap 8 respecting gear housing 4.

The bearing and intermeshed gearing of the drive shaft 6 and the driven shaft 11 correspond generally with the disclosure of the patent above identified. The inlet and outlet ports 12 and 13 are also similar to the disclosure of Patent 2,279,136. The respective shafts are connected by gears 14 and 15 to rotate in unison. They have seals at 17 and 18 in the gear housing and pump housing. Their splined ends 19 and 2% receive the hubs 21 and 22 of the respective impellers 23 and 24.

The impellers are identical and each is provided with three lobes 25.

It will be observed that the several lobes 25 are offset from the hubs on which they are mounted. They operate in generally annular chambers formed between the outer periphery of the pump housing 7 and the integral sleeve portions 26 and 27 which are coaxial with the shafts.

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The arcuate notch 28 in the sleeve 26 which encircles shaft 6 is concentric with the axis of shaft 11, while the notch 29 in sleeve 27 is concentric with the axis of shaft 6.

The center distance between the axes of shaft 6 and shaft 11 must be such with reference to the radius and the arcuate extent of the peripheries of the several lobes that the outer periphery of each lobe of impeller 24 will have bearing engagement with the arcuate surface of the notch 28, while the outer periphery of each lobe 25 of impeller 23 will have bearing engagement with the arcuate surface of the notch 29.

Moreover, the relationship between the parts must be such that the lobe 25 of one impeller will reach bearing engagement with the sleeve which is within the opposite impeller before such opposite impeller loses bearing engagemeut with the sleeve which is coaxial with the first mentioned impeller. This relationship clearly appears in Fig. 3 which shows a lobe 25 of impeller 23 engaged with the surface of sleeve 27 at notch 29, while a lobe 25 of impeller 24 is simultaneously engaged with the surface of sleeve 26 at notch 28. The device may be operated to rotate the impellers in either direction without in any way affecting this relationship. The pump is, therefore, reversible.

It is not possilbe to reduce the internal diameters of the sleeves 26 and 27 to any great extent below that shown without a corresponding decrease in shaft diameter. Yet relative shaft diameter decrease below that which is illustrated will be inexpedient, because the reduction in shaft strength will so reduce the capacity of the pump that it may cease to have commercial value.

For the foregoing reasons, among others, the production of a tri-lobed pump of this sort, long sought but thought impossible, has become possible only through the discovery of relative dimensions which maintain the seal requisite for pumping action without impairing shaft strength or otherwise destroying the commercial practicability of the pump.

The relationship between the parts can best be exemplified specifically by giving actual dimensions of the only production device available.

In this device the overall height of the casing is ten inches, the mid point between the two shafts is 5% inches above the base and'the axes of the two shafts are respectively 1.65 inches above and below the mid point. The inlet and outlet ports open into the casing at the level of the midpoint.

The clearance between the axes of the respective shafts is therefore 3.3 inches; the radius of each rotor is 2%.; inches. it will be observed that the lobes have concavely curved side surfaces. These are drawn to conform to a cylinder 2 5 inches in diameter, segmental wall portions of which form the sides of consecutive lobes. The length of a chord connecting the outer corners of each lobe is 1.75 inches.

The overall diameter of the housing sleeve portions 26 and 27 about which the respective lobes operate is 2 /2 inches.

The impeller wings or lobes are degrees apart. Their radius must be such that the outer periphery of each lobe strikes an are at 28, 29 on the housing sleeve which is concentric with the opposite shaft. This are cannot have greater angular extent than the angular extent of the inner end of the impeller lobe.

Assuming that the impeller diameter and the diameter of the housing sleeves 26 and 27 are known, the center distance between shaft centers should be such that the arcuate bearing surface provided by the notch in the periphery of each sleeve will have a chord about one-third the diameter of the sleeve. After these dimensions have been ascertained, the arcs forming the concave sides of A r V 1 2,836,125

the impeller wings or lobes'are generated to clear each other when the impellers: are in rotation in opposite directions. 7

Another approach to the-design of a three-lobed pump in accordance with the present invention is as follows: Assuming that the cylindrical chambers in which the tworoto'rs operate are of like diameter, the distance between the axes of the shafts 6 and 11 must begreat enough so that the are described by the outer periphery of the' lobe of one rotor will intersect the housing sleeve concentric with the other rotor within the sides of an equilateral triangle whose base has a length equal to the diameter of said sleeve and is disposed on the axis oi such other rotor and whose altitude is on the diameter which connects the axes of the respective rotors.

I claim: 7 t l. A pump comprising gear; connected shafts in spaced relation, means including a sleeve and a housing having "cylindrical wallsurfaces concentric with the respective shafts to define pump chambers of generally annular form, and tri-lobed rotors, each including a hub and equally spaced lobes having their centers 120 degrees apart carried by the hub and having bearing surfaces engaging cylindrical wall portions of the housing and the respective sleeves, opposite sides of the housing having inlet and outlet ports between the generally annular chambers aforesaid, each of said sleeves having a concave arcuatc bearing surface engaged by the outer peripheries of the :lobes of the rotor connected with the shaft other than;

that encircled by said sleeve, said bearing surface being 'located'between the sides'of an equilateral trianglethaving an'outside diameter of one of said sleeves as its base and having its altitude extending toward the axis of the other of said sleeves, the chord of said bearing surface being perpendicular to the altitude of the triangle and about one-third the length of the basethereof. V V,

2. The pump of claim 1, in which said bearing surface is locatedbetween the sides of an equilateral triangle having an outside diameter of one of said sleeves at its base and having its altitude extending toward the axis of the other of said sleeves for a distance equal to the radius of a pump chamber, the chords of said bearing surfaces of a length substantially equal to the width of the rotor lobes at the inside diameter of the rotors. r

3. The pump of claimpl in which said bearing surface is located between the sides of an equilateral triangle having an outside diameter of one of saidsleeves as its base and having its altitude on a line joining the axes of 'said sleeves and of a length equal to'the'radius of a pump chamber, the chord of, said bearing. surface being perpendicular to the altitude of the triangle and equal in length to the width of the rotor lobes at the inside diameter of the rotors, the leading edge of one rotor lobe entering a bearing surface before the trailing edge of another rotor lobe leaves such bearing surface 'for sealing between the rotors.

References Cited in the file of this patent V UNITED STATES PATENTS Great Britain Aug. 28, 1930 

